The invention relates to a single lens reflex camera using an electronic shutter, and more particularly to an apparatus for digitally displaying the amount of exposure in an automatic mode as well as that when the shutter speed is manually established.
In a single lens reflex camera using an electronic shutter, an A-D converter is used in the electronic shutter to provide a digital storage of a photometric value. Referring to FIG. 1 which schematically shows a conventional electronic shutter incoporating an A-D converter, light P which is transmitted through a photographic lens is converted into a voltage by a photoelectric transducer 1, the output of which is supplied to an analogue arithmetic unit 2 which provides a modification in accordance with the established film sensitivity (ASA-value) and F-value. The output of the arithmetic unit 2 is supplied to an A-D converter 3 through an automanual change-over switch S which is thrown to the auto position at this time. This switch actually comprises an electronic switch. The A-D converter 3 has a storage capability so that when a locking switch SF is closed, the photometric value from the arithmetic unit 2 is stored therein as a digital quantity. When the shutter is released, the locking switch SF is opened, whereby the photometric output stored in the A-D converter 3 is converted into seconds by means of a "second" counter 4 for operating a shutter operating magnet 5.
On the other hand, when the shutter speed is manually established, a desired shutter speed can be manually established by means of a variable resistor 6. In this instance, the A-D converter 3 and following components function automatically. Thus, a quasi-analogue voltage produced across the variable resistor 6 is applied to the A-D converter 3 through the electronic switch S in its manual position for operating the shutter in the similar manner as in the automatic mode. It will be noted that if the potential at the input b of the A-D converter 3 which is derived by the manual setting of the variable resistor 6 is equal to the potential at the output a of the arithmetic unit 2, there occurs no choice between the auto and manual modes, implying that a proper exposure is obtained Hence, when the shutter speed is manually established, the resulting amount of exposure can be displayed by a comparison of the potentials at the points a and b.